The Flu Fighters—in Your Food

While many people are still waiting for swine-flu vaccine to become available in their area, there is a lot they can do in their own kitchens to help fight off disease and build a strong immune system.

Scientists in the growing field of nutritional immunology are unveiling new evidence of the complex role that nutrition plays in fighting off infectious diseases like influenza. A diet rich in nutrients such as vitamin A, found in colorful fruits and vegetables, and zinc, found in seafood, nuts and whole grains, can provide the critical fuel the body needs to fight off disease, heal injuries, and survive illness when it does strike, experts say.

Scientists are still studying all the complex ways in which nutrients interact with the immune system. There is still much that they don't know about minerals such as zinc, for instance, including how they are absorbed and all the roles they play in the body. But scientists do know that certain vitamins and minerals can improve the body's ability to fight off infection: Studies in healthy elderly adults, for example, have shown an improved immune response to vaccination and fewer infections after receiving extra doses of vitamin E.

To create immune cells to fight off a specific infection, the body has to rapidly draw nutrients from the bloodstream, says Anuraj Shankar, a researcher at the Harvard School of Public Health. "If you don't have an adequate intake of vitamins and minerals, you won't be able to produce the number of immune cells you need, and the immune cells you do produce may be compromised," Dr. Shankar says. That makes it impossible to mount an effective response to infection, he says.

The benefits of good nutrition may have been recognized first by Hippocrates, the ancient Greek physician who declared "let food be thy medicine, and medicine be thy food." An 18th century naval surgeon's discovery that citrus fruits could cure scurvy in sailors was later recognized as a vitamin C deficiency, and after the 1930s, when dairies began to fortify milk with vitamin D, the disease known as rickets was virtually eliminated in the U.S.

Researchers warn that malnourished people may be a breeding ground for more dangerous infectious diseases. Animal studies at the University of North Carolina show that in a host with poor nutrition, viruses mutate in the face of a weak immune response to become more powerful. And once those mutations occur, even well-nourished hosts are susceptible to the newly virulent virus. "A lot of people may think malnutrition on the other side of the world isn't their problem," says Melinda A. Beck, a researcher at the University of North Carolina, Chapel Hill. But malnutrition "is a driving force in emerging infectious diseases that are spreading around the world," she says.

The human body doesn't have to be starving to suffer from malnutrition. Studies show that obesity, in addition to its other health risks, may also make people more susceptible to infections like the flu. A diet heavy on processed and fast foods may be low in the vitamins and minerals important for health. And diets that are high in saturated fat appear to actually depress the body's immune response, increasing the risk of infections.

Dr. Beck says studies of mice show that only 4% of lean animals infected with the flu virus die. That compares with a death rate of between 40% and 60% in obese mice infected with the virus. And after a small study showed that obese people vaccinated for the flu didn't mount a strong immune response, the University of North Carolina is expanding its trials to compare vaccination response rates in lean and obese people.